假设人们有理性预期。而且经济是黏性工资或黏性价格模型所描述的。解释为什么以下每一种命题都是正确的： a．

假设人们有理性预期。而且经济是黏性工资或黏性价格模型所描述的。解释为什么以下每一种命题都是正确的：

a．只有未预期到的货币供给的变动影响实际GDP。在工资和价格已经确定时，预期的货币供给的变动没有任何实际影响。

b．如果美联储在人们确定物价和工资的同时选择货币供给，这样，每个人都对经济状况拥有同样的信息，那么，货币政策就不能系统地运用于稳定产出。因此，保持货币供给不变的政策与根据经济状况调整货币供给的政策有同样的实际效应。(这被称为政策无关论(the policy irrelevance proposition))。

c．如果美联储在人们确定工资与价格之后决定货币供给，这样，美联储收集了有关经济状况的更多信息，那么，它就可以系统地运用货币政策去稳定产出。

Assume that people have rational expectations and that the economy is described by the sticky-wage or sticky-price-model. Explain why each of the following propositions is true:

a．Only unanticipated changes in the money supply affect real GDP. Changes in the money supply that were anticipated when wages and prices were set do not have any real effects.

b．If the Fed chooses the money supply at the same time as people are setting wages and prices, so that everyone has the same information about the state of the economy, then monetary policy cannot be used systematically to stabilize output. Hence, a policy of keeping the money supply constant will have the same real effects as a policy of adjusting the money supply in response to the state of the economy. (This is called the policy irrelevance proposition.)

c．If the Fed sets the money supply well after people have set wages and prices, so the Fed has collected more information about the state of the economy, then monetary policy can be used systematically to stabilize output.